Definition: bubbles

Before the second fermentation, the base wine is a liquid composed of water molecules, alcohol and aromatic compounds. These molecules are stacked on top of each other and bound together to ensure the cohesion of the whole. The conversion of sugar into alcohol by yeast causes the release of carbon dioxide. To do this, it must separate the molecules by working against the cohesive forces of the liquid. This is a difficult task that requires considerable energy, which the carbon dioxide molecule cannot mobilise on its own without external help. This help, called secondary nucleation or induced nucleation, is provided through processes known as heterogeneous or homogeneous. The homogeneous process is a family affair in which mother bubbles give birth to daughter bubbles. Why is the bubble spherical? When it is born, as it tries to find a place among the molecules of the liquid, the bubble must expend considerable energy, called interfacial energy. This energy is proportional to the surface area of the bubble. The sphere is the geometric shape that has the smallest surface area for a given volume. It is therefore the most efficient shape in terms of energy efficiency: the smaller the surface area of the bubble, the less work and energy it needs to grow. (L'Amateur de Bordeaux, special edition, December 1996) The release of carbon dioxide from sparkling wines creates a string of bubbles that rise to the surface of the glass. The bubbles form on tiny irregularities in the glass. This is why a wet glass generates fewer bubbles, and therefore less foam, than a dry glass. Some champagne flutes have a frosted spot on the bottom of the bowl. A string of bubbles will escape from it. The quality of a sparkling wine is measured by the fineness of the bubbles and their continuous renewal.